Fluid limit switch



June 6, 1967y M. A. NoTH 3,324,262

FLUID LIMIT SWITCH Filed April 9, 1965 United States Patent O 3,324,262 FLUlD L1B/11T SWITCH Myron A. Noth, Asheville, N.C., assignor to Square D Company, Park Ridge, lil., a corporation of Michigan Filed Apr. 9, 1965, Ser. No. 447,035 11 Claims. (Cl. Zilli-83) This invention relates to an air limit switch, that is, a limit switch operative to make or break an electric circuit when a moving object interrupts an air stream flowing between an air supply nozzle and the air inlet orifice of a pressure switch, and more particularly to an air limit switch having improved means for preventing the entry of foreign material into the orifice of the pressure switch.-

When air limit switches are used in locations where the surrounding atmosphere is contaminated with suspended particles of dust or dirt, or where other foreign material is apt to fall into the air stream between the air supply nozzle and the orifice of the pressure switch, some of the foreign material is carried into the switch orifice by the operating air stream eventually resulting in malfunctioning of the limit switch. In an air limit switch in accordance with the present invention, improved means are provided to deflect foreign material from the operating air stream and to trap any undeflected foreign material before it reaches the switch orifice.

In ac-cordance with this invention, foreign material is deflected from the air stream for an air limit switch by an improved air inlet means for directing operating air to the switch orifice. The air inlet means includes an airdeflecting means operative to deflect a portion of the air in the main air stream and causing it to flow in the reverse direction as a tubular backstream closely surrounding the main air stream. The tubular backstream carries much of the foreign material away from the main air stream and thus prevents the foreign material from-entering the switch orifice. In a modification, the improved air inlet means also includes an openable trap. Any remaining foreign material that inadvertently enters the entry end portion of the air inlet means notwithstanding the action of the backstream is forced by the operating air stream into the trap, the operating air stream flowing to the switch orifice in a passage at an angle to the direction of flow of a portion of the operating air stream entering the trap.

It is an object of this invention to provide an improved air limit switch.

Another object is to provide an air limit switch having improved means for restricting the entry of foreign material into the orifice of a pressure switch forming part of the limit switch.

A more detailed object is to provide an air limit switch having means causing the main air stream to be surrounded by a tube of air moving in a direction opposite to the main air stream thereby tending to keep foreign material out of the operating air stream.

Another object is to provide an air limit switch having improved means for trapping foreign material contained in the operating air stream thereby to prevent it from reaching a pressure switch forming part of the limit switch.

A further detailed object is to provide an air limit switch with a trap disposed axially of an operating air stream emitted from a nozzle and with a passage for a portion of the operating air stream to enable operating air to flow toward the orifice of a pressure switch in a direction at an angle to the path of the air flowing into the trap.

FIG. l is a front elevational view of an air limit switch in accordance with this invention with a portion of the casing of the pressure swltch broken away to show part of the operating mechanism thereof;

FIG. 2 is an enlarged sectional view of a portion of the structure of FIG. l taken generally along the line 2 2 of FIG. l;

FIG. 3 shows a modification of the limit switch of FIG. l.

Referring to FIGS. 1 and 2, an air limit switch in accordance with this invention comprises a nozzle assembly 10 which is operative to direct air under pressure from an air source 11 toward an air inlet means 12 for a pressure switch 14.

The nozzle assembly 10 preferably comprises a conduit 15 leading from the source 11 and connected by a pipe coupling 16 to one end of a nipple 18 retained in a suitable support 19 by means of nuts 20. A nozzle 21 having an aperture 24 is secured to the other end of the nipple 18 by means of a pipe coupling 22. Preferably, the aperture 24 is many times longer than its diameter so that a main air stream 25 emitted from the nozzle 21 remains relatively narrow for a considerable distance from the nozzle 21, as at 25a, and starts to spread slightly, as at 25h, as it approaches the air inlet means 12. As will be explained, to provide the desired shape of the air stream and the desired speed of operation, the air inlet means 12 and the nozzle assembly 10 are spaced from each other a distance related to the pressure of the air at the nozzle 21, the diameter and length of the aperture 24, and the response characteristics of the pressure swit-ch 14.

The pressure switch 14 may be of any suitable type but, to permit rapid operation of the air limit switch, should be capable of rapid recycling. Further, to provide for flexibility in the use of the air limit switch, the pressure switch 14 should be adjustable as to the minimum pressure which will effect initial operation.

The pressure switch 14, of a well-known type, has the foregoing capabilities and comprises a casing 26, a mounting structure 28, a diaphragm assembly 29, an operating mechanism 30, and a snap switch 31. The operating mechanism 3G and the snap switch 31 are disposed within the casing 26. An open side of the casing 26 is closed by a mounting plate 32 of the mounting structure 28 which structure also includes a pair of mounting feet 34 suitably secured to the plate 32 as by screws 35, a gasket 36 being interposed between the casing 26 and the plate 32.

Electrical connections (not shown) to the snap switch 31 are conveniently made through a bushing 38 surrounding an opening in the casing 26. The snap switch 31 may be either single or double pole and is operated by depression and by release of a self-restoring button 39 responsive to movement of an arm 4f) of an operating lever 41 forming part of the operating mechanism 30.l To effect depression and release of the button 39 in response to movement of the arm 40, the arm 40 carries an adjustable set screw 40a positioned to engage the outer face of the button 39. The operating lever 41 is pivoted on a shaft 42 and is biased by a range spring 44 disposed between an adjsutable stop 45 and a base portion 46 of the lever 41. The bias of the range spring 44 is such that the set screw 40a on the arm 40 normally holds the button 39 depressed against its self-restoring bias. The adjustable stop 45 comprises a spring seat 47 carried by a threaded shaft 49 which is journalled in a hole in a wall of the casing 26 and terminates outside the casing 26 in a knurled head 50.

Movement of the lever 41 about the pivot shaft 42 with and against the bias of the range spring 44 is caused by reciprocal movement of a pin 51 having a conical end portion received in a conical recess 52 in an outer face of the base portion 46 of the lever 41. The pin 51 is secured at its opposite end to the common center of a circular pressure plate 54 and flexible diaphragm 55 forming part of the diaphragm assembly 29. The pressure plate 54 is disposed against the fiexible diaphragm 55 which is fastened throughout its periphery between mating rim portions 56a and 57a, respectively, of a pair of dished members 56 and 57 to define inner and outer air chambers 58 and 59, the outer member 57 having a central orifice 60 constituting an inlet orifice for the pressure switch 14.

Operating air entering the orifice 60 under pressure impinges on the diaphragm 55 thereby to move the pin 51 inwardly so as to pivot the operating lever 41 against the bias of the range spring 44. An adjustment or calibration spring 61 surrounding the pin 51 is seated at its inner end against an adjustment nut 51a threaded on the pin 51 and at its outer end in a recess in the face of the member 56. The spring 61 urges the pin 51 and, hence, the pressure plate 54 to the left. The length of the spring 61, as selected by adjustment of the nut 51a, determines the minimum pressure in the chamber 59 that will cause movement of the lever 41 against the bias of the range spring 44. The inward movement of the pin51 pivots the lever 41 about its pivot shaft 42 so that the set screw 40a carried by the arm 40 moves away from the button 39 allowing the switch 31 to operate. A suitable stop (not shown) may be provided to limit movement of the arm 40 away from the switch 31. Diminution of pressure in the outer chamber 59 allows the spring 44 to return the lever 41 to its initial position, the set screw 40a then depressing the button 39 to operate the switch 31.

In accordance with this invention, air flowing from the nozzle assembly is caused, by the air inlet means 12, to enter the chamber 59 and impinge on the diaphragm 55. The air inlet means 12 comprises a centrally flanged tube 62 secured at an inner end by threaded reception within an annular socket 64 which, in turn, is secured to the member 57 so that an opening through the tube 62 and the socket 64 is aligned with the orifice 60. An air deflector 66 having an inner portion 67 of reduced diameter is secured on an outer end portion of the tube 62 by a coupling 68. The dellector 66 also has an outer barrier portion 69 of enlarged diameter provided, in its outer face, with an annular recess 70 defining a central boss 71 through which an aperture 72 extends. The aperture 72 is aligned with and communicates with the aperture of the tube 62 and with the orifice 60.

In the operation of the air limit switch shown in FIGS.

1 and 2, air under pressure emitted in the main air stream 25 from the nozzle 10 enters the aperture 72 and flows through the tube 62 and the orifice 60 into the chamber 59 thereby to impinge upon the flexible diaphragm 55. This forces the diaphragm 55 and the pressure plate 54 inwardly, causing the pin 51 to effect pivotal movement of the lever 41 so that the arm 40 moves away from the button 39 to permit the switch 31 to operate. If air stream 25 is interrupted, as by an article passing therethrough, the spring 44 pivots the lever 41 against the bias of the spring 61 causing the arm 40 to move toward the button 39 which is then depressed by the set screw 40a to cause the switch 31 to operate. l Ordinarily, the main air stream 25 would tend to carry foreign material into the aperture 72 and thence through the tube 62 and orifice 60 into the chamber 59. To reduce the amount of foreign material in the air stream, the recess 70 in the deflector 66 intercepts the outer periphery of the main air stream 25, as at 25C, and dellects a portion of the air stream in the opposite direction in the form of a somewhat diverging tube 25d disposed about the main air stream 25. Foreign material in the atmosphere surrounding the limit switch is thus carried in a direction away from the aperture 72 and is thereby prevented from entering the main stream 25 and being carried thereby into the chamber 59.

Although the air limit switch may be made in various sizes, most efficient operation results when certain relationships areV maintained between the pressure of the air at the nozzle 21, the diameter and length of the nozzle aperture 24, the distance between the eXit end of the aperture 24 and the detlector 66, and the pressure response 4characteristics of the pressure switch 14. With a nozzle aperture 24 having a length of 0.75 inch and a diameter of 0.094 inch, and a pressure at the nozzle 21 of from two to twelve p.s.i., three to five inches has been found to be a satisfactory distance between the nozzle 21 and the dellector 66, with the deector having a diameter of 1.25 inches.

In the modification of FIG. 3, the dellector 66 is secured as by the coupling 68 to one arm 74 of a pipe T 75. Another arm 76 of the T 75 is connected by couplings 77 and 78 and a tube 79, which may be formed of plastic, to the annular socket 64. A third arm of the T is connected by a coupling 81 to a trap 82 closed at its outer end by a removable plug 84 having a small vent opening 84a. The body of the trap 82 preferably is a short length of metal pipe.

In the operation of the embodiment of FIG. 3, the deflector 66 performs as in FIGS. 1 and 2 to create a tube 25d of air about the main air stream 25. Air entering the aperture 72 causes a pressure to be built up in the tube 79 leading from the arm 76 thereby to cause deflection of the diaphragm 55 and the operation of the switch 31 as in the embodiment of FIGS. l and 2. Any foreign material carried into the aperture 72 notwithstanding the action of the reverse flowing air tube 25d is not carried upwardly by the operating air stream into the chamber 59 but, instead, passes through the arm into the trap 82 where it may be periodically removed upon removal of the plug 84.

Although the limit swtch has been described as being responsive to an air stream, it is obvious that the switch could be of the type operable by fluids generally and that the inlet means and its associated deflector would be operative when used in connection with gases other than air or with liquids.

Having thus described my invention, I claim:

1. A limit switch comprising nozzle means emitting a stream of fluid under pressure, a pressure switch having a fluid inlet orifice, a fluid inlet means having a guiding aperture disposed in said stream of fluid and communicating with said orifice for directing a portion of the fluid in said stream into said inlet orifice, and said inlet means aidditionally having a deflector disposed in said stream adjacent the entry end of said guiding aperture, said deflector having a groove opening toward said stream of fluid and being so positioned and shaped that at least a part of the remaining portion of said streams of fluid is deflected adjacent to said stream toward said nozzle means.

2. A limit switch comprising nozzle means emitting a stream of uid under pressure, a pressure switch having a fluid inlet orifice, a uid inlet means having a guiding aperture disposed in said stream of fluid and communicating with said orice for directing a portion of the fluid in said stream into said inlet orifice and said inlet means additionally having a deflector disposed in said stream and surrounding said guiding aperture, said deflector having an annular groove opening toward said stream of fluid and being positioned and shaped so as to deflect substantially the remaining portion of said stream of fluid generally toward said nozzle means and in the form of a tube of fluid surrounding said stream.

3. A limit switch in accordance with claim 1 wherein said fluid emitted from said nozzle is air.

4. An inlet means for a pressure switch of a fluid limit switch, said inlet means comprising means defining a guiding aperture for directing operating -uid to the pressure switch, a deflecting barrier disposed adjacent the entry end of said guiding aperture, a groove ina surface of said barrier positioned and shaped so that, when fluid is directed toward said guiding aperture, a portion of the fluid is deflected away from said guiding aperture in the direction from which fluid is directed toward said guiding aperture.

5. An inlet means in accordance with claim 4 characterized in that a trap is operatively disposed in said inlet means between an entry end of said guiding aperture and said pressure switch.

6. An inlet means for a pressure switch of a fluid limit switch, said inlet means comprising a fluid deflector having a central portion and a barrier portion surrounding and coaxial with said central portion, an aperture extending through said central portion and opening on opposite sides of said central portion to permit the passage of fluid therethrough, and an annular groove in said barrier portion co- -axial with said aperture for directing liuid away from said aperture in a tubular path generally coaxial with said aperture.

7. An inlet means in accordance with claim 6 characterized in that said groove has a generally semi-circular radial cross-section.

8. A limit switch in accordance with claim 2 characterized in that said nozzle means is provided with a discharge aperture having a length substantially greater than the diameter of the discharge aperture.

9. A limit switch in accordance with claim 8 wherein the nozzle means is so spaced from the inlet means that substantially all of said stream of fluid from said nozzle means impinges on said inlet means.

10. A fluid pressure responsive limit switch comprising a pressure switch having an inlet orilice, a fluid inlet means mounted on said pressure switch and including a guiding aperture having an entrance end and an exit end with the exit end communicating with said orifice, and said inlet means additionally including a deflecter having an annular groove surrounding said guiding aperture and opening in the same direction as said entrance end of said aperture, said groove being so shaped and positioned that when a stream of fluid is directed toward the inlet means, a portion of said stream is directed into said orice and at least a part of the remaining portion of said stream is dellected adjacent to said stream in a direction opposite to the direction of said stream.

l1. A fluid pressure responsive limit switch in accordance with claim 10 wherein said pressure switch comprises a casing, `an operating mechanism disposed within said casing, a diaphragm assembly including a exible diaphragm aligned with said orifice so that said portion of the stream of Huid directed into said orifice impinges on said diaphragm and causes movement thereof, said operating mechanism including an operating lever pivoted on said casing and rockable about its pivot axis in response to movement of said diaphragm, and an electrical swit-ch disposed within said casing and operative in response to rocking of said operating lever.

References Cited UNITED STATES PATENTS 1,628,723 5/1927 Hall ZOO- 83 2,8 16,7018 12/ 1957 Menoher 235-92 3,106,894 10/1963 Johnsen 200-83 X BERNARD A. GILHEANY, Primary Examiner. H. B. GILSON, G. MAIER, Assistant Examiners. 

1. A LIMIT SWITCH COMPRISING NOZZLE MEANS EMITTING A STREAM OF FLUID UNDER PRESSURE, A PRESSURE SWITCH HAVING A FLUID INLET ORIFICE, A FLUID INLET MEANS HAVING A GUIDING APERTURE DISPOSED IN SAID STREAM OF FLUID AND COMMUNICATING WITH SAID ORIFICE FOR DIRECTING A PORTION OF THE FLUID IN SAID STREAM INTO SAID INLET ORIFICE, AND SAID INLET MEANS ADDITIONALLY HAVING A DEFLECTOR DISPOSED IN SAID STREAM ADJACENT THE ENTRY END OF SAID GUIDING APERTURE, SAID DEFLECTOR HAVING A GROOVE OPENING TOWARD SAID STREAM OF FLUID AND BEING SO POSITIONED AND SHAPED THAT AT LEAST A PART OF THE REMAINING PORTION OF SAID STREAMS OF FLUID IS DEFLECTED ADJACENT TO SAID STREAM TOWARD SAID NOZZLE MEANS. 